This invention relates to a spinner which is, for example, used to apply a resist, liquid developer or the like to a wafer in the manufacture of semiconductor devices and, more particularly, to an improved structure of a cup of the spinner.
The spinner (which is also called "developer", according to its use) generally comprises a rotating spindle for causing a workpiece, such as a wafer, to spin at a high speed and a cup disposed about the rotating spindle. The workpiece is caused to spin within the cup at a high speed by the rotating spindle, while a liquid agent to be applied, such as resist, is sprayed onto the workpiece by means of a nozzle. As a result a film having a thin and uniform thickness is formed on the workpiece by virtue of the action of centrifugal force caused by the high speed of spinning. In a typical structure, for the purpose of avoiding bad influences caused by air in the interior of the cup and by the splashing of the agents to be applied, the cup is provided in the bottom wall thereof with a port for evacuation of air in the interior of the cup during the operation of the spinner.
In a conventional spinner, however, there is the problem that, in the case of applying the resist to a wafer, for example, various defects, such as an unevenness in application of the agents (commonly called "firework"), and an adhesion of resist balls and resist filaments, are apt to occur. It is understood that such defects depend on an interrelationship between a condition of an air current in the interior of the cup, that is produced by the spinning of the wafer as well as the evacuation of air, and the viscosity of the resist. For example, in a case where the viscosity of the resist is relatively low, if the rate of air evacuation is too high, an unevenness in application, i.e. "firework", is produced. This defect can be prevented from occurring by reducing the rate of air evacuation. In this case, however, there are problems, such as the production of resist balls, due to splashing of the resist from the inner wall of the cup, and an unevenness in the thickness of the film, due to an unevenness in the air evacuation. Therefore, reduction in the rate of air evacuation is not a practical and useful solution.
For ensuring a proper and even rate of air evacuation, a structure of the spinner cup has been used in which the cup is provided with a deflector ring and a base ring, or the like (for example, "Wafertrac", manufactured by GCA Co.). The deflector ring and the base ring are disposed on the upper side and the side adjacent to the bottom wall of the cup with the wafer positioned therebetween, and they are formed integrally with the cup or are attached securely to the cup. The deflector ring is normally formed to extend inwardly towards the central region of the cup interior, so as to substantially surround the periphery of the wafer, whereby the current of air to be evacuated is deflected and becomes even to a certain extent in the circumferential direction. The base ring is provided with a plurality of holes for air evacuation arranged approximately equidistantly in the circumferential direction. Through these holes the interior of the cup is communicated with the evacuation port formed in the bottom wall of the cup. According to this structure, since the air evacuation is effected through a plurality of evacuation holes formed in the base ring, the air evacuation can be effected approximately evenly in the circumferential direction, even though the cup is provided in the bottom wall with only one evacuation port. It is also possible to determine the number and size of the evacuation holes in the base ring so that a proper rate of air evacuation is provided.
However, in the structure of the cup provided with at least the deflector ring as mentioned above, there is the following problem. In the case where the rate of air evacuation is small or the evacuation holes are blocked up when a resist of a high viscosity (more than about 45 cp) is applied, the rate of air evacuation from the interior of the cup is reduced. Accordingly, the air current produced by the spin of the wafer collides with the inner wall of the cup and the deflector ring, so as to produce an ascending air current which flows out of the cup through an opening formed in a top cover of the cup. In this case, the resist splashes from the inner wall of the cup and the surface of the deflector ring so as to produce resist balls, and the resist applied to the surface of the deflector ring is thrown up by the ascending air current to produce resist filaments. Then, when the spinning of the wafer has been stopped, the ascending air current disappears, whereby the resist filaments fall and adhere to the surface of the wafer. For preventing the above mentioned defects from occurring, a method can be used in which the rate of air evacuation is increased and the evacuation holes in the base ring are made larger in diameter so as to prevent them from being blocked up. According to this method, however, in the case where the resist has a low viscosity of about 30 cp, the rate of air evacuation is too high and results in the occurrence of "firework", as mentioned hereinbefore. Therefore, such a method is not a good solution.
Finally, in the conventional structure of the spinner cup, there is the problem that, in relation to the viscosity of the agents to be applied, such as the resist, too high a rate of air evacuation results in the occurrence of the uneveness of application, i.e. "firework", and, on the contrary, too low of a rate of air evacuation results in the production of resist balls, due to splashing of the resist, and of resist filaments, due to the ascending air current.